1. Field of the Invention
This invention relates to a cassette loading apparatus most suitably applied, for example, to a professional-use video tape recorder of the front loading type, and particularly to a driving system for a cassette holder.
2. Description of the Prior Art
A cassette loading apparatus for a video tape recorder of the front loading type is conventionally arranged so that, as disclosed, for example, in U.S. Pat. No. 4,664,337, a cassette holder having a cassette inserted therein is first drawn in horizontally from a cassette receiving position to an intermediate position and then moved vertically downward to transport the cassette from above to a cassette playing position. Various mechanisms for achieving such movement of the cassette holder are known, including, for example, the mechanism disclosed in U.S. Pat. No. 4,320,424 wherein a plurality of rollers mounted on a cassette holder are guided by L-shaped guides in a pair of guide plates disposed on opposite sides of the path of travel of the cassette holder while L-shaped racks provided integrally on the cassette holder are driven by a pair of pinions mounted on the guide plates. Another example of such mechanisms is disclosed in U.S. Pat. No. 4,933,790 wherein a guide pin of a cassette holder is driven directly by means of a pivotal arm mounted on a guide plate.
In recent years, cassette loading mechanisms for professional-use video tape recorders have required a long operation stroke for the cassette holder, that is, a long horizontal stroke for drawing in a cassette from a cassette receiving position to a cassette playing position so that a cassette of any of a plurality of different sizes (large, medium and small) may be played on the video tape recorder. It is also necessary to retain a cassette of any one of the different sizes in the cassette playing position with a stabilized resilient urging force.
However, in order to achieve an increased stroke for a cassette holder, it is necessary for the conventional cassette loading apparatus as described above to have L-shaped racks with an increased horizontal length or a pivotal arm with an increased length. However, if the horizontal length of the L-shaped rack or the length of the pivotal arm is increased, then the space required for movement of the same may extend significantly beyond the space required for movement of the cassette holder, which will significantly increase the overall size of the cassette loading apparatus. Therefore, it is difficult to achieve a long stroke for the cassette holder. Further, with the conventional cassette loading apparatus described above, the cassette is resiliently urged to the cassette playing position by means of a torque limiter incorporated in the driving system for the pinons or for the pivotal arm. However, since the resiliently urging force upon the cassette varies significantly with a small displacement of the cassette holder at the cassette playing position, it is necessary to effect a fine adjustment of the position of the cassette holder. Moreover, another problem is that a locking mechanism must be provided because, when the cassette is resiliently urged to the cassette playing position, a reactive force from the torque limiter is applied to the driving system.
Cassette loading apparatus for a video tape recorder of the front-loading type are also known which allow observation of how much tape remains to be wound in the cassette being recorded or reproduced by the video tape recorder. For example, one such conventional cassette loading apparatus includes a reflecting mirror supported for pivotal motion around a horizontal axis above the intermediate position of the cassette holder with a movable end of the mirror in contact with the cassette holder. When the cassette holder moves downwardly to the cassette playing position, the reflecting mirror tilts downwardly by its own weight so that it is inclined by 45 degrees or so, in order to reflect an image of the upper face of the cassette from the cassette playing position to the cassette insertion opening. In this way, the amount of tape remaining to be wound can be observed through the insertion opening.
In such cassette loading apparatus, in order to achieve a long operation stroke of the cassette holder as described above, it is necessary to dispose the reflecting mirror at a position that is rather close in the cassette inserting direction to the intermediate position and so is rather distant from the cassette insertion opening.
However, in such conventional loading apparatus, since the pivotal reflecting mirror is supported directly on the cassette holder, it is difficult to dispose the reflecting mirror at a position that is displaced to a great extent in the cassette inserting direction from the cassette receiving position of the cassette holder. Accordingly, even if a long stroke of the cassette holder is achieved, the reflecting mirror must be disposed a position in proximity to the cassette insertion opening, so that the field of view of the upper face of the cassette at the cassette playing position is restricted significantly.
Further, in such a cassette loading apparatus of the type as described just above, a cassette at the cassette playing position is often brightly illuminated from above by a lightbulb provided within the video tape recorder so that the cassette may be observed.
However, the conventional bulb used for internal illumination suffers from a short life and is vulnerable to vibrations, shock and the like.
A light emitting semiconductor device such as an LED (light emitting diode) seems to be an alternative to the bulb for the purpose of internal illumination. However, a light emitting semiconductor device such as an LED emits light in a sharply limited direction and fails to illuminate uniformly, so that an LED is not suitable as an internal illuminating element.
Incidentally, the cassette loading apparatus for a video tape recorder the front-loading type disclosed in U.S. Pat. No. 4,664,337 mentioned hereinabove is designed for use in a broadcasting station and includes a cassette insertion guide for positioning the cassette holder a cassette of any one of a plurality of predetermined sizes. The apparatus also includes a cassette size detecting lever for detecting the size of the cassette in the cassette holder, and a cassette size detecting switch mounted for operation by the cassette size detecting lever. The distance between a pair of reel receivers is automatically adjusted in accordance with the size of the cassette inserted in the cassette holder.
However, this cassette loading apparatus is disadvantageous in that the number of parts and the number of steps required for assembly are great and the cost is high.
Another cassette loading apparatus for a professional-use video tape recorder of the front loading type is disclosed in U.S. Pat. No. 4,631,607 which is commonly assigned with the present patent application.
This cassette loading apparatus also is arranged for transporting a cassette of any one of a plurality of different sizes (large, medium and small) to a cassette playing position. The cassette loading apparatus includes a cassette urging plate of a size sufficient to cover the upper face of a cassette of any one of the different sizes. The cassette urging plate is disposed above and normally biased to contact with the cassette holder by means of a cassette urging spring such that a cassette of any one of the different sizes is inserted between the cassette holder and the cassette urging plate against frictional resistance exerted by the biasing force of the cassette urging spring. When the cassette holder is drawn in horizontally from the cassette receiving position to the intermediate position with the cassette inserted between the cassette holder and the cassette urging plate, the cassette slides on the cassette urging plate, and then when the cassette holder is moved vertically downward to the cassette playing position to load the cassette from above to the cassette playing position, the cassette urging plate is resiliently urged downwardly by the cassette urging spring. Thus, the cassette at the cassette playing position is resiliently urged from above to the cassette playing position by the cassette urging plate.
In this cassette loading apparatus, however, since the single cassette urging plate is used commonly for cassettes of different sizes, if the cassette urging force by the cassette urging plate is set so as to resiliently urge the small cassette with a suitable resilient force, then the resiliently urging force will be insufficient for the large cassette. Accordingly, the cassette urging force by the cassette urging plate must be set so as to assure a sufficient resiliently urging force for the large cassette.
When the cassette resiliently urging force is set for a cassette of the large size, a correspondingly great cassette inserting force is required when a cassette of any one of the different sizes is inserted between the cassette holder and the cassette urging plate, and insertion of a cassette may possibly be difficult. Further, when a cassette is inserted or when the cassette holder is drawn in horizontally, the cassette is rubbed against the cassette urging plate with a great force, and the cassette is liable to be scraped. Further, due to warping or the like of the cassette urging plate or of the cassette, a stabilized cassette urging force cannot be obtained that is appropriate to the size of the cassette inserted.